1. Field of the Invention
This invention relates to electrical connectors, especially as involving transient signal suppression electrical connectors and Electromagnetic interference (EMl) filtering electrical connectors.
2. Description of the Prior Art
U.S. Pat. No. 4,600,262 to Neiman et al discloses an electrical connector in which one or more electrical circuit components are mounted on the side of each contact, rather than surrounding the contact body as in prior art filter connectors, such as disclosed in U.S. Pat. No. 3,670,292 to Tracy where the filter element on each contact is of complete cylindrical form.
Present transient suppression connectors such as that disclosed in U.S. Pat. No. 4,729,743 to Farrar et al and in U.S. Pat. No. 4,746,310 to Morse et al which contain both transient suppression means as well as filtering means, perform the transient suppression and filtering functions in a serial or in-line fashion, in which the transient suppression means are mounted on the forward portion of each contact and the filter means are disposed on the rearward portion of the contact. This serial design adds to the overall length of the connector and may be unacceptably long for some end users.
Close examination of the aforementioned patents reveals that relatively small diodes are used due to the space limitations and mounting manner in which the diodes are placed. These diodes are rated at no more than 500 to 600 watts at room temperature. For a breakdown voltage rating of 10 volts, this produces a current handling ability of 50 to 60 amps, which is more than adequate for most applications. However as the breakdown voltage rating increases, the current handling ability decreases as a function of power divided by voltage. Thus for a breakdown voltage ration of 100 volts, this produces a current handling ability of only 5-6 amps. At higher temperatures, the power rating of a transient suppression diode is reduced even further. For many applications requiring survivability to lightning or other high voltage pulses such as electrical systems in composite aircraft might see or for electrical systems operating at higher temperatures, this current ration is much too low.
For additional current handling ability, prior art suggests placing transient suppression diodes in parallel between the contact and the grounding plate as suggested by Nieman et al in the previously mentioned patent in which the diodes are placed at either end of the outwardly bowed leaf spring or by Couper et al in U.S. Pat. No. 4,582,385 where the diodes may be placed on opposite sides of the contact. However, if there is even a small voltage breakdown difference between the nominally rated diodes, for a given transient, the diode with the lower breakdown voltage will begin conducting first, carrying the bulk of the transient current until its clamping voltage increases (due to an increase in its temperature from the upper dissipated) and the other diode begins conducting. Thus there exists an opportunity for the first diode to be damaged by the transient. Since most transient suppression diodes fail in the short circuit mode rather than the circuit mode, damage may occur in the very electronics that the device was intended to protect.
Transient suppressing diodes have an inherently high level of capacitance, usually between 300-2000 pF. This capacitance is acceptable and even desirable for low to medium frequency signals where high frequency filtering is required. However, for high frequency digital signals of 1 MHz and above, this level of capacitance is unacceptable, causing excessive degradation of the digital signal.